In many areas of science it may be important to supply image sequences of an object of interest to a viewer. In the case that the object of interest is moving periodically it may be interesting to compare image sequences acquired at different points in time. Particularly in some areas of medicine it may be important to compare the behaviour of a moving organ as for example the heart or the lungs before and after a certain event.
For example, in interventional cardiology which deals with catheter-based diagnosis and treatment of heart diseases stents may be placed in coronary arteries to improve the oxygen rich blood delivery to the micro-vasculature of the heart muscle. After an intervention outcome validation is needed to estimate the effect and success of the treatment and to determine follow-up medication and/or the use of other therapies. A check if there is an increase of the arterial blood flow and an increase of myocardium perfusion after placing the stent is not easy because the heart beating rate is often different from before the treatment.
A known method for comparison between the arterial blood flow and perfusion before and after stenting is Thrombolysis In Myocardical Infraction (TIMI) Frame Count. The comparison is achieved by counting the frames from the moment a contrast agent (CA) is entering the vessel under investigation until the full filling of the vessel or until the contrast agent starts entering the muscle tissue like for example the myocardium.
The comparison which may be achieved by counting frames is not as accurate as may be desired. Furthermore, the comparison result achieved in this way is indirect and only provides an approximate quantitative number. For example, a possible result of TIMI Frame Count is increased blood flow after stenting. However, when the heart rate is different compared to pre-stenting, a mis-interpretation of the clinical outcome can easily occur.
There may be a need for a method or apparatus for correlating two frame sequences of a periodically moving object with respect to the periodicity which correlation allows for an improved direct comparison of the frame sequences.